Discussion

Aural rehabilitation through a hearing aid is a safe, conservative and non-surgical option preferred by many patients with hearing impairment. Hearing aid fitting is preceded by the creation of an ear mould. However, the process, if not managed carried out with caution, can lead to complications in patients with altered aural anatomy. The silicone impression material used for making an ear mould is viscous, and hence can flow into the mesotympanum, hypotympanum and Eustachian tube, leading to poor middle-ear aeration.^{Reference Suzuki, Okamura, Yano, Moteki, Kitoh and Takumi2}

Persistence of a foreign body in the middle ear can cause complications such as bleeding from the ear, otitis externa, perforation of the tympanic membrane, permanent hearing loss, stapes dislocation, ossicular discontinuity, ossicular erosion, facial nerve palsy, granulation tissue in the middle ear, aural polyps and endolymphatic fistula.^{Reference Kiskaddon and Sasaki3} Clinical presentations of a foreign body in the middle ear include otalgia, aural fullness, otorrhoea, vertigo, facial nerve palsy and hearing loss acceleration.^{Reference Jacob, Morris and Welling1,Reference Usmani, Singh, Pandey and Agarwal4} Inflammation of the external auditory canal, debris, granulation tissue and perforation of the tympanic membrane are the usual findings on clinical examination. Imaging studies may be helpful in evaluating the nature, location and extent of the foreign body in the middle ear.

Jacob et al. reported a child with retained ear mould impression material that had flown into the middle ear via a ventilation tube during the preparation of swim moulds.^{Reference Jacob, Morris and Welling1} Usmani et al. reported a case of a vegetative foreign body in external auditory canal that had migrated to the middle ear after multiple attempts of inadvertent removal by a local physician, causing tympanic membrane perforation and facial nerve palsy.^{Reference Usmani, Singh, Pandey and Agarwal4} A case of a neglected foreign body in the middle ear that triggered the formation of cholesteatoma and acute mastoiditis was reported by Garag et al.^{Reference Garag, Rashmi, Shanbag and Arunkumar5} Similarly, a case of a bullet in the external auditory canal was reported by Piromchai et al., where the bullet was pushed through the tympanic membrane into the hypotympanum during an attempt to remove the foreign body. The patient was later referred to an otolaryngologist and the bullet removed by a post-auricular approach.^{Reference Piromchai, Srirompotong, Lertchanaruengrith and Mills6} Hence, any foreign body in the ear has to be managed carried out with caution by an experienced otolaryngologist, to avoid iatrogenic complications.

The choice of surgical approach for foreign body removal from the middle ear depends on the nature and extent of the foreign body. van den Boer et al. recommended several surgical approaches for foreign body removal from the middle ear.^{Reference van den Boer, Spronsen, Holland, Ebbens and Waterval7} Forty-nine ears with similar case scenarios were analysed. In their study, in-office removal attempts without high-resolution computed tomography of the temporal bone were described in 12 patients, of which only 1 was successful. A transcanal approach was chosen in 35 patients, a transmastoidal approach with or without posterior tympanotomy was selected in 9 patients, and subtotal petrosectomy was opted for in 1 patient. They also recommended canaloplasty as a useful approach for the removal of a foreign body in the hypotympanum with a prominent anterior canal wall.^{Reference van den Boer, Spronsen, Holland, Ebbens and Waterval7} Katarkar et al. preferred a post-aural approach, as it provides wide exposure of the medial part of external auditory meatus and middle ear.^{Reference Katarkar, Katarkar, Jain, Modh and Shah8}

The hearing aid moulding procedure should be performed by a well-trained hearing aid specialist. Otolaryngologists, audiologists and other hearing instrument dispensers must be aware of the potential hazards associated with the ear moulding procedure. It is highly recommended that the audiologist take a brief otological history, focusing on the patient's history of ear discharge and previous ear surgery. If the anatomy is altered or should the audiologist be in doubt, the patient needs to be referred to an otolaryngologist for further evaluation. For instance, to get an ear mould impression of a large and deep mastoid cavity, the cavity must be packed with otoblocks under microscopic guidance by a trained otolaryngologist.

We recommend a clinical approach algorithm for audiologists, for prior to taking an ear mould impression, in cases when the patient directly consults them without seeing an otolaryngologist (Figure 6). This approach can significantly reduce the risk of complications associated with the ear moulding procedure.

Fig. 6. Clinical approach algorithm for audiologists, for before taking an ear mould impression. TM = tympanic membrane